The present invention relates to a semiconductor device in which an interposer formed of a tape conforming with the thinning of a semiconductor substrate or an insulating film including an insulating substrate is used as a holder of a lead.
In a semiconductor device, thinning of a semiconductor element is being promoted in an attempt to achieve a high density assembly. Also, a plurality of thin semiconductor elements are stacked one upon the other in many cases for the actual use. The thin packages known to the art include, for example, a TSOP (Thin Small Outline Package), a TCP (Tape Carrier Package) and a BAG (Ball Grid Array).
FIGS. 1A and 1B are a plan view and a cross sectional view along the line IB—IB, respectively, collectively showing a semiconductor device of a conventional structure. A silicon chip having a thickness of 250 μm to 625 μm is used as a semiconductor element (chip) 1. A polyimide film 2 having a thickness of 75 μm is used as an interposer for supporting the chip 1 and holding a lead wire 3. The polyimide film 2 has an opening portion 6. One end portion of the lead wire 3, which is formed of, for example, a copper thin film, protrudes into the opening portion 6 so as to be connected directly to a connecting electrode (pad) 4 formed on the surface of the chip 1, with the other end portion projecting outward from the polyimide film 2.
That portion of the lead wire 3 which projects outward from the polyimide 2 constitutes an outer lead that is connected as an external connecting electrode to an external circuit. The other portion of the lead wire 3 constitutes an inner lead. For connecting the lead wire to the semiconductor element, known is a method of using a TAB tape, in which bumps are formed on the pads and a large number of lead wires are subjected to a bump bonding at a time. Also, a liquid resin such as an epoxy resin is dripped within the opening portion 6, which includes the connecting portion between the pad 4 and the lead wire 3, of the polyimide film 2 formed on the chip 1 and so as to form a resin molding 5.
In a package using an interposer, the connection between the interposer and the chip is achieved by a lead wire performing an electrical connection. The interposer and the chip arranged apart from the interposer are supported by the lead wire, and the reliability of the package such as the mechanical strength and the moisture resistance is improved by the resin molding applied later. As described above, the resin molding is performed in the prior art after the chip and the lead wire are connected to each other. However, where the distance between adjacent lead wires is large, the interposer tends to peel off the resin molding in the prior art. The peeling tends to be increased so as to give rise to the crack occurrence in the resin molding.
The crack is likely to bring about a lead cut-off, giving rise to a problem in respect of the visual appearance and the reliability. Further, where the distance between the adjacent lead wires is large, the lead wire is twisted during the period between the connection of the lead wire and the resin molding. Particularly, the lead wire distribution tends to become sparse where the number of pins is small relative to the chip size.
Further, where the thickness of the chip is small, i.e., about 50 μm, the chip is thinner than the polyimide film used as the interposer. If a resin molding is formed under such a condition by dripping a resin by means of potting, the resin is attached in an amount larger than required so as to form a thick semiconductor device, resulting in failure to achieve the object of decreasing the thickness of the semiconductor device. Under the circumstances, it is widely employed nowadays a method of attaching a back sheet to the polyimide film and the chip, followed by coating the connecting portion between the chip and the lead wire positioned on the back sheet with a resin by a printing technique so as to form a resin molding. Even in this case, it is impossible to overcome the difficulties leading to the lead cut-off such as the crack occurrence and twist of the lead.